O.K., here it is!
Here is the Soft Halyard with extra Diamond Knots. It might not be clear, but the tails on the loop with stop knots end just out of the picture, and the other end of the line with the eye splice/shackle ("connector line") is about a foot long and has another eye splice on the other end. One end of the connector line gets put over a stop knot, the other goes to the hook on the scale, so as to pull it with the come-along.
Here is the test rig. Note that the "connector line" has been hooked to the s-hook on the scale, and the eye/shackle has been put on the last stop knot on the luggage tag which is attached to a bolt on the table.
Here are the results
Here's what they look like
Basically, out of 7 tests, 6 of them broke at the end of the bury in the splice and one of them reached almost 100%. After doing 20 splices in a row, they get much quicker, and I was making more of an effort on the taper, so they got better. Because I am lazy, and I was doing a lot of splices in order to just break them, I did not do any sewing or whipping on any of the splices. They would have to be sewed to stay in place under light loads.
On the first pull, the first diamond knot broke, at about 375Lbs, not sure why, but the rest of them lasted, all the way up to 500Lbs, and it was the first knot, rather than any of the ones closer to the loop. It may be that that particular diamond knot was not well made, or that it had suffered wear and tear from the last 10 test pulls wherein other parts of the assembly broke
I am convinced that the diamond knots farther from the loop are as strong as the ones closer to the loop, which is what I hoped to prove.
It occurs to me that I could build a soft shackle with multiple diamond knots to make it of adjustable size.